First, you need to have a good understanding of the LOTR lore. Read the books and watch the movies multiple times. Then, think about the characters you want to focus on. It could be a well - known character like Frodo or a lesser - known one. Next, come up with a unique plot. Maybe something that wasn't fully explored in the original works, like the daily life in Rohan during the war. After that, start writing your first draft, don't worry too much about grammar at first.
Well, starting a lotr fanfic can be exciting. Firstly, immerse yourself in the world of LOTR. Listen to the soundtracks, look at fan art, and read fan theories. This will give you inspiration. Decide whether you want to write a prequel, sequel, or a story set during the main events. If you choose a prequel, think about events that could have led to the main story. For instance, how did Gollum first find the Ring? For a sequel, consider what happened to the characters after the destruction of the Ring. And when you start writing, write in a style that is true to the LOTR universe, with a touch of your own creativity.